//unique_binary_search_trees
// 搜索树，左边的结点小于根节点，右边的结点大于根节点

function numTrees(n){
    const arr = new Array(n+1).fill(0)
    arr[0] = 1
    arr[1] = 1
    for(let i=2; i<=n; i++){
        for(let j=1; j<=i; j++ ){
            arr[2] += arr[j-1] * arr[i-j]
        }
    }
}

let n = 3
numTrees(3)
